Blow-in door actuation for afterburner nozzle

ABSTRACT

THE BLOW-IN-DOORS FOR AN EXHAUST NOZZLE ARE HELD IN OPEN POSITION BY AN AIR PISTON THAT PERMITS THE DOORS TO CLOSE WHEN A PREDETERMINED PRESSURE DIFFERENTIAL IS BUILT UP ON THE DOORS. THE AIR PRESSURE FOR ACTUATING THE PISTON MAY BE A SELECTED COMPRESSOR PRESSURE SO THAT THE PRESSURE VARIES WITH ENGINE OPERATING CONDITIONS AND THUS THE REQUIRED PRESSURE FOR CLOSING THE DOORS WILL VARY CORRESPONDINGLY.

Nov. 14, 1972 A, HASBROUCK ETAL 3,702,681

BLOW-IN-DOOR ACTUATION FOR AFTERBURNER NOZZLE Filed April 7, 1971 2 Sheets-Sheet 1 5y www BLow-IN-Dooa ACTUATION FOR AFTERBURNER NozzLE Filed April 7, 1971 NOV. 14, 1972 A, HASBRQUCK EI'AL 2 SheetsSheet 2 l IIIIIIIIHHI Nw, MN uw Nwll United States Patent O 3,702,681 BLOW-IN DOOR ACTUATION FOR AFIERBURNER NOZZLE Augustus Hasbrouck, Middletown, and Lawrence J.

Lauck, South Windsor, Conn., assignors to United Aircraft Corporation, East Hartford, Conn.

Filed Apr. 7, 1971, Ser. No. 131,972 Int. Cl. B6Sh 25/46 U.S. Cl. Z39-265.17 7 Claims ABSTRACT OF THE DISCLOSURE The blow-in-doors for an exhaust nozzle are held in open position by an air piston that permits the doors to close when a predetermined pressure differential is built up on the doors. The air pressure for actuating the piston `may be a selected compressor pressure so that the pressure varies with engine operating conditions and thus the required pressure for closing the doors will vary correspondingly.

BACKGROUND OF THE INVENTION Unless the blow-in-doors are held in open position, they are not necessarily in the proper position for the start of engine operation and they do not close in unison, not only because of the position of the doors about the axis of the nozzle with some being held closed by the weight of the door and others remaining opened, but also because of the pressures existing on opposite sides of the blow-in-door during certain engine operations. The use of a spring acting on each door to hold it in open position is not satisfactory in certain instances since the spring applies an increasing load on the door as the latter approaches closed position and thus requires a higher and higher pressure inside the row of doors to close them, A constant force acting on each door throughout its movement from open to closed position is considered most desirable.

SUMMARY OF THE INVENTION One feature of the invention is an air spring connected to the blow-in-doors to apply substantially a constant opening moment on each door throughout its travel. Another feature is the control of the air pressure as a function of engine operation as by supplying a selected compressor pressure to the air spring. Another feature is the positioning of the air spring in the struts that are provided in the nozzle construction between adjacent blowin-doors thus minimizing the space requirement for the device.

According to the invention, the blow-in-doors for the variable area nozzle are held in open position by an air spring device which permits the blow-in-doors to close l when the pressure differential across the doors reaches a predetermined amount. This pressure differential may be a function of engine operation by pressurizing the air spring from a selected point in the compressor since this pressure varies under different conditions of engine dlight operation. Preferably for the requirements of space, the actuating device is located in the supporting struts that are positioned between adjacent blow-in-doors and connect the secondary nozzle to the primary nozzle supporting structure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an external perspective view of an engine with parts broken away.

FIG. 2 is a longitudinal sectional view showing the afterburner nozzle construction.

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FIG. 3 is a fragmentary sectional view similar to FIG. 2 but showing the construction between adjacent blow-indoors.

FIG. 4 is a transverse sectional view substantially along the line 4-4 of FIG. 2.

FIG. 5 is a longitudinal sectional view substantially along the line 5-5 of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention is shown in connection wtih a turbofan engine which includes an outer duct 2, FIG. l, within which is positioned a fan 4 at the front end of a conipressor 6. The latter is positioned within the duct 2 and discharges through a diffuser 8, a burner 10, and a turbine 12. At the downstream end of the duct 2 is the nozzle construction 14 forming an extension of the duct 2.

Referring now to FIG. 2, the downstream end of the duct 2 terminates the afterburner duct 16 within which is positioned the afterburner liner 18. The primary nozzle 20 consisting of a plurality of illaps 22 surrounds and projects beyond the end of the afterburner duct. These flaps are pivotally mounted at their upstream ends to a movable actuating ring 24, the latter being moved axially through a plurality of actuating rods 26 connected to the ring and positioned radially around the downstream end of the duct 16. The actuation mechanisms for these rods is well known and needs no description.

The nozzle ilaps are supported on a plurality of guide rollers 28 `mounted on a frustoconical ring 30 the latter being secured through cleats 32 to an inner primary nozzle support structure 34, the: latter extending forwardly and terminating in a ring 35 surrounding the duct 2 and attached thereto.

Attached to the supporting ring 35 are a plurality of struts 36, FIGS. l and 3, which extend in circumferentially spaced relation to one another from the ring 35 to a secondary support ring 38 on which the secondary nozzle flaps 40 are mounted. The function and actuation of the secondary daps is not a part of the present invention and need not be described in detail. It is sufficient to note that the primary nozzle 20 forms a convergent variable area nozzle at the downstream end of the afterburner duct and the secondary nozzle flaps 40 form a convergent-divergent nozzle projecting downstream of the primary nozzle.

Between the two nozzles are positioned a plurality of blow-in-doors 42, FIGS. 1 and 2, located between the struts 36 and pivotally mounted at their upstream ends as best shown in FIG. 2. The purpose of these blow-indoors is well known. Such devices have been described previously as for example in the Hamilton Pat. 3,062,003. The present invention is concerned with the actuation of these doors.

As above stated, the blow-in-doors are individually supported for pivotal movement on supporting pins 44 carried by a support ring 46 attached to the ring 35. The blow-in-doors are caused to move inwardly for the admission of ambient air external of the duct 2 into the space between the primary and secondary nozzles under appropriate conditions of engine static and ilight operations.

As best shown in FIGS. 2 and 4, each blow-in-door 42 has adjacent each edge thereof a bracket 48 with an axial slot 50 therein. This bracket is spaced substantially from the pivot pin 44 as shown in FIG. 2. A lever 52, having a pin 54 at one end received in the slot 50, is secured at its opposite end to a shaft 54 located in a boss S6 in the strut 36 and also carrying an actuating link 58 located within the hollow strut 36.

Also positioned within the strut as shown in FIGS. 2, 3 and 4 is an air cylinder 60 supported to pivot on a transverse axis by a bolt 62. The cylinder has a piston 64 with a projecting piston rod 66, the latter ending in a yoke 68. The yoke is connected by links or cables 70 to the free ends of the adjacent arms 58 on opposed shafts 54 as best shown in FIG. 4. Air under pressure is admitted to the inner or upstream end of the cylinder as by the conduit 72, FIG. 2, thereby urging the blow-in-doors into open position.

In order to provide a suitable pressure for actuating the blow-in-doors the conduit 72 is connected as best shown in FIG. l to the upstream or high pressure end of the compressor 6 there being a tap 74 provided at this point. In this way an adequate pressure is supplied so that the blow-in-doors are held in open position during those portions of the engine cycle where it is desirable to have air entering the openings provided by the blow-in-doors. It will be understood that as the aircraft in which the engine is mounted is operating at high altitudes the pressure available at the tap 74 is lower because of the surrounding atmospheric pressure and accordingly the doors are held in open position by a lower piston pressure than would prevail if the engine were operating at sea level. Furthermore, depending upon the position of the power level for the engine that is to say whether the engine is operating at idle or at full power, the pressure available at tap 74 also varies. Accordingly, the pressure supplied to the air cylinders varies to a great extent as a function of engine operation and it is this change in pressure that makes the operation of the blow-in-doors more effective by using as the source of air pressure a location in the engine in which the pressure will vary in relation to the engine operation.

Furthermore, the air pressure during a steady-state engine condition exerts a constant pressure on the piston in any position of the piston so that each blow-in-door is held in open position by a constant piston pressure. This is much in contrast to the use of a spring for holding the blow-in-doors in open position since the spring would provide, as above stated, an increasing force as the blowiti-door traveled toward and into closed position.

By locating the actuating cylinder and the blow-in-door linkages Within the struts positioned between adjacent blow-in-doors the actuating mechanism is stowed in a much smaller space to accomplish the desired result than would be required if it were necessary to have the actuating mechanism external thereto. It will 'be apparent that, by adjustment of the several arms of the actuating linkage, the desired inward moment acting on the doors may be adjusted so that the compressor discharge pressure will bear the proper relationship to the air pressure acting directly on the doors to close them so that the doors will close appropriately at the proper time in the cycle of engine static or ight operation and will move fully from opened to closed position when the appropriate pressure differential exists on the doors without requiring a buildup of pressure to overcome a spring force as has been customary previously. The linkage 70 may be a cable extending from the yoke 68 to the actuating arms so that one door may move to some extent independently of the adjacent door since with a pair of cables in this arrangement one of the blow-in-doors may move faster toward closed position than the other.

We claim:

1. An aircraft engine including a compressor, burner, turbine, and exhaust nozzle, said exhaust nozzle including a primary, variable-area nozzle having a support structure, a secondary variable-area nozzle downstream of said primary nozzle and having a secondary support structure, and blow-in-doors positioned axially between said two nozzles, in combination with means including a cylinder and piston for moving said blow-in-doors between closed and opened position and means for supplying air under pressure to the side of the piston urging the blow-in-doors into open position.

2. A device as in claim 1 in which the air cylinder is supplied by air from a selected position in the compressor.

3. A device as in claim 2 in which the selected position is substantially at the discharge end of the compressor.

4. A device as in claim 1 including axially extending struts connecting the secondary support structure to the primary support structure with the blow-in-doors positioned between the struts and with the actuating cylinder and piston for said doors positioned in said struts.

5. A device as in claim 1 including a linkage connected to each blow-in-door and a connection from the linkage to the piston.

6. An exhaust nozzle for an aircraft engine including a primary, variable-area nozzle having a support structure, a secondary, variable-area nozzle downstream of said primary nozzle and having a secondary support structure and blow-in-doors positioned axially between said two nozzles, axially extending struts connecting the secondary support structure to the primary support structure with the blow-in-doors positioned between the struts, in combination with cylinder and piston means for moving said blow-in-doors between closed and opened position, means for supplying air under pressure to the end of the piston urging the blow-in-doors into open position and means connecting the piston to said blow-in-door, there being an actuating cylinder and piston for each of the blow-indoors.

7. An exhaust nozzle as in claim 6 including a linkage connecting each blow-in-door to the associated actuating cylinder and piston, and a connector from the linkage to the piston so positioned that the connector is loaded in tension when the piston is acting to hold the blow-in-door in open position.

References Cited UNITED STATES PATENTS SAMUEL FEINBERG, Primary Examiner U.S. Cl. X.R. 

